Blood flow restriction training involves exercise whilst using a pneumatic cuff to restrict blood flow, similar to a blood pressure cuff. The decreased oxygen to the muscle, in combination with reduced ability to get rid of waste products from the exercise (e.g. lactic acid), causes the muscle to work a lot harder than without occlusion.
The muscle is forced to adapt to the strenuous conditions, by increasing in size and strength, irrespective of the lighter weight being used. The advantage of this approach is that to improve muscle strength you don’t have to use heavy weights, which can often aggravate injuries due to the high load through the joint.
Blood flow restriction may in theory be very beneficial in people with musculoskeletal pain who need to get stronger to improve the management of their condition but pain stops completing an adequate gym program.